1. The Field of the Invention
The present invention relates generally to directional antennas. More particularly, the present invention relates to an antenna comprising a linear array of parallel fed dipoles.
2. The Background Art
With recent advances in computer and communications technology and their associated work and lifestyle changes, rapid and accurate telecommunications and data transmission have become increasingly important. One very important method of transmitting data has been through direct radio communication using a transmitter and a receiver. Both the transmitter and the receiver use an antenna to transmit or receive a signal. Accordingly, there are many forms of antennas which have been devised to increase the power and directivity of signal transmission and reception. For example, microwave dishes are used in the communications industry to carry telephone messages and other information over long ranges. Internet connections have also been provided using directional broadband equipment which broadcasts data to subscribers.
With the advent of computer networking, it has become desirable to send directional data over relatively short distances with low power. In the United States, for example, certain broadcast frequency ranges are open to unlicensed use, so long as the broadcast power is kept below a certain range. For example broadcasting in the range of 2400 MHz to 2500 MHz requires no FCC license so long as the broadcast power is below 1 watt. Unfortunately, many known directional antennas such as microwave and satellite antennas are much too expensive to use for short range, low power signal transmissions. Other types of straight or looped antennas can be used for these short range transmissions but many of these configurations suffer from interference and static when they are transmitting such a low power signal. Moreover, if the low power signal is not properly directed, its range, and hence the usefulness of the antenna, can be greatly diminished because a substantial portion of the broadcast energy is wasted, rather than being sent where it is needed.
It has been recognized that it would be advantageous to have a low power directional antenna which is balanced omni-directionally, with high directivity and broad bandwidth, and that is also simple in design.
The present invention advantageously provides a parallel fed colinear dipole array antenna for broadcasting and receiving a signal of a selected wavelength. The antenna comprises a plurality of elongate dipole antennas attached end-to-end in a linear array. A power divider divides and transmits an in-phase signal in parallel to each of the dipole antennas. The linear spacing of the dipoles is selected such that the signals of the dipole antennas interfere with each other so as to focus signals which propagate substantially perpendicularly to the linear array, and to diminish other signals.
In accordance with one aspect of the present invention, the plurality of dipole antennas are interconnected by a plurality of dipole spacers comprising a dielectric material such as Delrin, ABS, or styrene. More particularly, the length of the spacers may be selected such that the ends of the dipoles are separated by an effective distance equal to about one sixth of the selected wavelength.
In accordance with another aspect of the present invention, the length of the dipoles is selected to match the characteristic impedance of the dipoles with the impedance of the transmission. lines. The antenna may more particularly comprise an array of four dipoles.
In accordance with another aspect of the present invention, each of the plurality of elongate dipole antennas may comprise first and second colinear electrically conductive tubes, such as thin-walled copper tubing. A gap spacer comprising dielectric material may be disposed between the first and second colinear tubes.
In accordance with another aspect of the present invention, the power divider may comprise a Wilkinson divider having an input connection for receiving a signal, a plurality of conductive pathways interconnected to the input connection, each conductive pathway having an effective length equal to about one half the selected wavelength. A plurality of drive lines may be associated with the power divider, each line connecting one of the plurality of dipole antennas to one of the conductive pathways of the power divider. The drive lines may have a length equal to an integer times about one half of the selected wavelength.
Additional features and advantages of the invention will be set forth in the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate by way of example, the features of the invention.